Cycle-time watchdog

Foundation capability (taktora-executor v0.1): visibility into deadline-missed events at the dispatch layer.

Feature: Cycle-time watchdog FEAT_0014
status: open
satisfies: FEAT_0010
is satisfied by: REQ_0030, REQ_0031
is implemented by: BB_0028

Visibility into deadline-missed events at the dispatch layer.
Requirement: Subscriber deadline detection REQ_0030
status: implemented
satisfies: FEAT_0014
is verified by: TEST_0118
links outgoing: BB_0028, TEST_0118

The runtime shall provide a TriggerDeclarer::deadline(subscriber, deadline) declaration that fires the item if no event arrives at the subscriber within deadline.
Requirement: Per-execute timing visibility REQ_0031
status: implemented
satisfies: FEAT_0014
is verified by: TEST_0119
links outgoing: BB_0028, TEST_0119

The runtime shall report each item’s actual execute duration through ExecutionMonitor::post_execute(task, started_at, took, ok).